10 inch brakes, new shoes and the drum locks on when it's screwd up tight.

[alien]

Ok brains trust I need your help.
I've got a '79 Series3 ex British army air portable(lightweight) that I'm fitting new brakes to.
It's got 10" drums all round with a vacuum assisted duel circuit master cylinder.
The hoses are imperial not metric as expected with a S3, possibly due to parts compatibility with previous MOD delivered S2a's.

The previous owner fitted new brakes to the rear as they where hanging on, it now needs new shoes on one side.
He changed the wheel cylinders but I believe the problem is the flexible hose delaminating.
The front brakes need replacing, leaking wheel cylinders and low contaminated shoes.

This is where I'm stumped.
I fitted new shoes after checking them against the old ones, they look identical excluding lining thickness although marginally narrower.
As I slip the drum on every thing feels good, not tight and the drum rotates freely.
However as I fit the 3 screws to nip the drum up the last 3/16" the drum locks and can't be rotated.
I've chamfered the outer lining edge thinking it was possibly rubbing on the drum.
I've put bearing blue on the outer edge of the linings and there is no contact with the drum so not jamming the linings against the backing plate.
Refitting the old linings eliminates the issue.
This happens on all 4 wheel with the new linings.
Today I fitted the front wheel cylinders and hoses, the shoe issue remains.

Any suggestions as I can't see why it's occurring?
My next idea is to file a little off the leading and trailing ends of the linings to see if it's the cause.
I need to order 2 sets of linings to finish the brake rebuild but want to identify why it's happening first.

TIA, cheers Kyle.

[Tins]

Ok brains trust I need your help.
I've got a '79 Series3 ex British army air portable(lightweight) that I'm fitting new brakes to.
It's got 10" drums all round with a vacuum assisted duel circuit master cylinder.
The hoses are imperial not metric as expected with a S3, possibly due to parts compatibility with previous MOD delivered S2a's.

The previous owner fitted new brakes to the rear as they where hanging on, it now needs new shoes on one side.
He changed the wheel cylinders but I believe the problem is the flexible hose delaminating.
The front brakes need replacing, leaking wheel cylinders and low contaminated shoes.

This is where I'm stumped.
I fitted new shoes after checking them against the old ones, they look identical excluding lining thickness although marginally narrower.
As I slip the drum on every thing feels good, not tight and the drum rotates freely.
However as I fit the 3 screws to nip the drum up the last 3/16" the drum locks and can't be rotated.
I've chamfered the outer lining edge thinking it was possibly rubbing on the drum.
I've put bearing blue on the outer edge of the linings and there is no contact with the drum so not jamming the linings against the backing plate.
Refitting the old linings eliminates the issue.
This happens on all 4 wheel with the new linings.
Today I fitted the front wheel cylinders and hoses, the shoe issue remains.

Any suggestions as I can't see why it's occurring?
My next idea is to file a little off the leading and trailing ends of the linings to see if it's the cause.
I need to order 2 sets of linings to finish the brake rebuild but want to identify why it's happening first.

TIA, cheers Kyle.

I would love to give you the "correct" answer, Kyle, but all I can tell you is that at a Base Workshop, brake shoes were always "radiused" prior to fitting ( there was a jig expressly for this purpose ). I doubt that this is the recommended practice, but it was done. I never had anything to do with 'lightweights', but I doubt their brakes were different to the standard cars. We could never fit brake shoes without doing this. It was only a few thou".
However, I suppose you have checked that the adjusters are all wound back. Try giving each shoe a tap in towards the axle with a mallet ( not a hammer ) and see if that helps. The old shoes fit because they already did!

[alien]

I would love to give you the "correct" answer, Kyle, but all I can tell you is that at a Base Workshop, brake shoes were always "radiused" prior to fitting ( there was a jig expressly for this purpose ). I doubt that this is the recommended practice, but it was done. I never had anything to do with 'lightweights', but I doubt their brakes were different to the standard cars. We could never fit brake shoes without doing this. It was only a few thou".
However, I suppose you have checked that the adjusters are all wound back. Try giving each shoe a tap in towards the axle with a mallet ( not a hammer ) and see if that helps. The old shoes fit because they already did!
The adjuster is OK and it's strange the drum fits over the linings easily for all but the last 1/4"or less.
I'll do a rough grind on the ends of the linings to see if it helps, these lining are not going to be used so a play wont hurt.

Radius grinding maximises shoes face to drum contact so is the preferred method, be it at the loss of some lining thickness.

[JDNSW]

I would check whether the drums are not worn a bit tapered, possibly due to loose wheel bearings. (Calipers should tell)

Similarly, check that the shoes are sitting straight in a sideways sense. Early backing plates had an adjustable steady post, later ones are pressed and not adjustable. In either case, wear on this could result in uneven wear on both the drums and the old shoes.

But perhaps the most likely problem is that you have the springs incorrectly assembled so that the shoes are not pulled against this steady. This is likely to give the result you see.

[alien]

Thanks John,
Wheel bearings have no movement in them when I went over it for seeing what was needed to get it roadworthy.
It has the later backing plate so no adjustment and only low mileage so doubt they are the issue.
I've been going through a Series 1/2 manual I have and found the spring have been fitted right correctly but the anchor ring was on the wrong shoe
on 2 of the 4 wheels.
They will be fitted to the trailing shoes as they go back together.


So tonight I grabbed the angle grinder out took the leading and trailing edge of the linings on the pair of shoes I had chamfered the edge on as they are throw away items anyway.
This solved the issue so johntins was on the money with the need to radius grind them.
The other set where still on the rear and a close examination showed faint rub marks on the 3 of the 4 ends of the linings.
As the drum has been squared to the hub it's bound at the anchor point buy the look of things.
I've filled a leading edge starting at 1/2 the lining height and about 1" along the face of the lining on both the leading and trailing edge of both shoes.
I refitted them and now the drum spins freely with the screws tightened, it's an extremely rough way of doing a radius grind.
So I have another set of shoes on order and I'll see if they present the same problem but for now the mystery has been solved thanks to AULRO.

[Homestar]

Hi mate, only just saw the message you left on my phone on the weekend. [bigwhistle]

Looks like you've got the problem sorted - when I did the 101 brakes recently, I radiused the shoes for that by gluing (with spray adhesive) some course sandpaper into the drum then rubbing the shoes inside until I had contact all the way accross them - only took a couple of minutes and was a lot less harsh and mor accurate than getting a file or grinder out. Sandpaper peels out and the glue cleans up easily with thinners.

Oh and Cam is back home and on the mend - thanks for asking. [smilebigeye]

[Tins]

when I did the 101 brakes recently, I radiused the shoes for that by gluing (with spray adhesive) some course sandpaper into the drum then rubbing the shoes inside until I had contact all th way accross them - only took a couple of minutes and was a Lo less harsh and mor accurate than getting a file or grinder out.



Now, that is a good idea.

[JDNSW]

Now, that is a good idea.

I agree entirely - I would never have thought of it!

Luckily some of us are bright.

[Homestar]

Thanks - not something I would have done with old asbestos linings but ok now (I still wear a dusk mask though when doing this).